The Keening Gloom

Just beyond the light of the Radiant Citadel rages the Keening Gloom, a massive ethereal cyclone. Nothing that enters the cyclone is seen again.
  When explorers rediscovered the Citadel, the Keening Gloom hungrily circled the city. Its endless howl struck terror in their hearts and engulfed several adventurers. After the heroes entered the Citadel and reawakened its power, the cyclone was driven back. But in times of turmoil within the Citadel, the cyclone ominously draws closer.
  Scholars have studied the Keening Gloom for decades but have only theories about its nature, its connection to the Radiant Citadel, and what befalls those caught in its terrible throes. Many fear the cyclone cannot be held at bay forever.